Picking the strongest 2007 snowmobile engine in the class is easy. Last year, we named the new-at-the-time Liberty 600 HO engine as the class powerhouse and it went on to be the quickest 600 classer at the Snow Week/DynoTech Research Shootout in Woodgate, New York. With 2007’s CFI hardware installed on the same engine, we know Polaris is in the ballpark on its 125 hp claim. This engine is stronger, and the other snowmobile engines in the class were not updated for this season.

Polaris markets the peak horsepower, but the company is underselling where we see the best benefit. The mid-range, corner-to-corner punch is stronger on the new engine and will be more appreciated by its riders. The engine loves to rev and the fuel delivery doesn’t have a glitch. The Liberty 600 HO CFI will be the strongest 600 on the market.

While no longer the leader in terms of power, the Rotax 600 H.O. SDI in the MX Z is the most linear and smoothest 600-class two-stroke engine. The Polaris engineering department was gunning for the MX Z 600 H.O. SDI in another performance category: fuel mileage. The Rotax engine is the industry’s gold standard for blending power and economy. Reports of sipping fuel at the rate of 20 mpg weren’t uncommon; obviously, a lot depends on how the machine is driven.

While not a formal test looking specifically at fuel consumption, it appeared during our test rides that the Polaris Liberty 600 HO CFI engine falls short of Ski-Doo’s benchmark. The Polaris used more fuel than the Rotax when it came time to refill them even though both machines were on the same trails, ridden by the same drivers and driven on the same day. The Polaris also upped the fuel cell to 11.7 gallons for added range, but its larger capacity was the first drained. The MX Z holds 10.6 gallons and 10 gallons fills the Nytro. This isn’t upsetting, though. It takes more fuel to make more horsepower, and the Polaris makes the most.

It’s hard to ballpark the Nytro’s fuel usage in this test. This … ahem … might be due to the Nytro accumulating more running miles than the other sleds when towing a machine that ran out of fuel. However, when running 2006 models with these same engines, we averaged 14.4 mpg with the Nytro and the Rotax engine averaged 16.8 mpg. We have no reason to suspect dramatically different results than these.
The Nytro fits the four-stroke stereotype: broad torque. The engine has all kinds of useable power regardless of what the tach reads. There never seems to be an instant hit of power that drivers feel from squeezing the flipper to WOT on a two-stroke. Instead, it’s a steady, rolling grunt that always seems to be on tap. The engine makes pleasing noises while doing it, too, and the engine pulls the machine to high speeds effortlessly.

Engine braking is still something to get used to on the Nytro. After switching machines back and forth, it took a few curves before our testers were at home on the Yamaha. In the twisty turns, there’s no need to touch the brake. Unload the throttle right before the turn to scrub down to the necessary entry speed, then get back on the gas for the turn.

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